Described in document WO 02/28959, in the name of the Applicant, is a grafted copolymer having polyamide blocks on a polyolefin backbone that is chosen from ethylene/maleic anhydride and ethylene/alkyl (meth)acrylate/maleic anhydride copolymers, forming a co-continuous nanostructured blend; this gives this copolymer exceptional thermomechanical properties, which are retained when redispersing this grafted copolymer in flexible polyolefins such as the flexible ethylene copolymers.
Such blends have applications as adhesives, films, tarpaulins, calendered products, electrical cables or powders for slush moulding processes for moulding objects.
These grafted olefinic copolymers having polyamide blocks are materials that show, however, mediocre aging resistance in oils, which limits their use in applications in the automotive field, such as parts “under the engine bonnet”.
The terms “resistance to oils” or “aging resistance in oils” of these thermoplastic compositions is understood to mean, on the one hand, the level of retention of the mechanical properties, in particular the elongation at break (EB) and the tensile strength (TS), measured in tension, after a period in oil and, on the other hand, the weight and volume swelling after immersion in these oils.
Document U.S. Pat. No. 5,278,229 describes an olefinic composition comprising:                (A) from 50 to 99.5% by weight of a polyolefin resin such as polyethylene or polypropylene;        (B) from 0.4 to 50% by weight of a saponified ethylene vinyl acetate copolymer; and        (C) from 0.1 to 15% by weight of a maleic anhydride-grafted ethylene copolymer that has reacted with a polyamide oligomer having a degree of polymerization >15.        
This composition is used in a multilayer structure as an oxygen barrier layer, but does not provide resistance to aging in oils.
Document EP 0 403 109 describes compositions composed of:                5 to 95% by weight of a saponified ethylene vinyl acetate copolymer;        95 to 5% by weight of a polyamide of which the terminal amine groups are predominant; and        0.5 to 10% by weight of a polyolefin modified by an unsaturated carboxylic acid, such as a maleic anhydride-modified polyethylene. These compositions are used to improve the stability of sheets or films formed by extrusion, while avoiding the formation of gels, and they comprise functionalized polyolefin levels of at most 10%.        
Document EP 1 022 309 describes compositions based on an ethylene/vinyl alcohol copolymer comprising by weight:                50 to 98% of an EVOH copolymer;        1 to 50% of a polyethylene (A), that may be an ethylene/alkyl(meth)acrylate copolymer; and        1 to 15% of a polymer (B) resulting from the reaction (i) of a copolymer (B1) of ethylene and of an unsaturated monomer X grafted onto or copolymerized with (ii) a copolyamide (B2). The amount of polymer (B), or functionalized polyolefin having reacted with the polyamide, is at most 15% by weight, or an amount well below that of the compositions of the invention.        
The objective of the invention is to provide a flexible thermoplastic composition based on functionalized polyolefins grafted by polyamides, which retains a good level of properties, especially in terms of elongation, tensile strength and weight and volume swelling, after aging in oils, all of these properties also being retained by the materials or objects obtained from such a composition.